The proposed work is an investigation of the mechanism of action of opiates and opioid peptides on single neurons of the myenteric plexus of the guinea-pig ileum. Tissue will be maintained in vitro and substances will be applied to neurons by iontophoresis and by bath application in known concentrations. Four major research objectives for the current period are as follows. First, to investigate the mechanism of the induction of tolerance and dependence by incubation of neurons in vitro in the presence of opiate agonists. Second, to study the effects of interference with the adenyl cyclase/cyclic AMP system in the action of morphine and opiods. Third, to study the mechanism of the action of naloxone in increasing the firing rate of neurons which are removed from tolerant/dependent animals. Fourth, to pursue further studies with intracellular recording from single neurons which indicate that the site of action of opiates and enkephalin is not on the soma of the neurons but on their more distant cellular processes.